Growth and major nutrient concentrations in Brassica campestris supplied with different NH4+/NO3- ratios

In the present study, we investigated whether growth and main nutrient ion concentrations of cabbage (Brassica campestris L.) could be increased when plants were subjected to different NH4+/NO3- ratios. Cabbage seedlings were grown in a greenhouse in nutrient solutions with five NH4+/NO3- ratios (1:0; 0.75:0.25; 0.5:0.5; 0.25:0.75; and 0:1). The results showed that cabbage growth was reduced by 87% when the proportion of NH4+-N in the nutrient solution was more than 75% compared with a ratio NH4+/NO3- of 0.5:0.5 35 d after transplanting, suggesting a possible toxicity due to the accumulation of a large amount of free ammonia in the leaves. When the NH4+/NO3- ratio was 0.5:0.5, fresh seedling weight, root length, and H2PO4- (P), K+, Ca2+, and Mg2+ concentrations were all higher than those in plants grown under other NH4+/NO3- ratios. The nitrate concentration in the leaves was the lowest in plants grown at 0.5: 0.5 NH4+/NO3-. The present results indicate that an appropriate NH4+/NO3- ratio improves the absorption of other nutrients and maintains a suitable proportion of N assimilation and storage that should benefit plant growth and the quality of cabbage as a vegetable.